Another major earthquake on the leading edge of the Australian Plate. Australia is rapidly moving north/northeast, shoving over the Pacific Plate, striking it at a 90 degree angle for that plate is moving northwest. And Asia is heading eastwards and the collision points are the island chains of Japan and the Philippines. There are many questions about the Australian Plate's geology.
Villages and towns in the Solomon Islands have been severely damaged and at least eight people are missing feared dead, after a powerful earthquake in the South Pacific caused a tsunami.
The earthquake struck 350 kilometres north west of Honiara at a depth of 10 kilometres.
Solomon Islands Broadcasting Corporation in Honiara said residents on Simbo Islands had reported waves travelling up to 200 metres inland.
The island of Gizo, a regional centre in the country's west, endured a wave several metres high which flattened houses and caused widespread damage.
Witnesses also reported villagers being washed into the sea.
Image from Sky News TV, Australia.
Once again, villages and towns were suddenly indunated by a tsunami and we won't know how many people were swept away, attempts at setting up tsunami warning systems are hampered by the lack of time one has if an earthquake happens right off shore.
This lastest mega-earthquake is, like the Boxing Day one, involved the fast moving India/Australia plate complex. Both of these land masses once hinged on Antarctica but a great rift opened up between all three of them and first India and then Australia broke loose and the ever-spreading sea floor has propelled them both northwards at a much faster clip than any other tectonic plates.
The 'Ring of Fire' caused by the Pacific Plate being shoved violently westwards by the rifting in the Atlantic Ocean shoving North America westwards causes all the volcanoes and earthquakes in the rim of Asia and North America but the Australian Plate is a totally different agent here: it is driving northeast at a mad clip and has already ridden over a good section of the Pacific Plate which is not being shoved northwards by the Australian Plate at all.
I drew a simple map that shows the general direction of plate movements. Note how North America is moving in a totally different direction from South America. Indeed, it looks like it is cartwheeling in a counter-clockwise motion. Eurasia, on the other hand, is moving in a clockwise direction towards the Pacific.
The question is, why are the two largest land masses on the northern hemisphere moving in a turning motion, towards one spot in the Pacific? We know they are being pushed but why in that particular direction? There is nothing at the North Pole that could be pushing them, is there? Antarctica is nearly totally stationary. Perhaps this is due to the heavy load of ice sitting on top. The earth isn't round and we have a moon that has enough gravitational pull to yank the huge oceans into high and low tides that are quite obvious on the ground.
We also have a widening Atlantic Ocean that is smaller than the Pacific. The weight of the oceans, the thinness of the ocean floors, the lithosphere, all these things affect the movement of the plates.
From temporary lunacy to werewolf awakenings, the lunar cycle has seen its share of blame. Now, scientists say that the different phases of the moon influence the flow of a massive ice stream in Antarctica.
The Rutford Ice Stream—a river of ice larger than the Netherlands which drains the West Antarctic Ice Sheet—varies its speed by almost 20 percent every two weeks, scientists report in the Dec. 21 issue of the journal Nature.
The change coincides to the bi-weekly tidal cycle when the gravitational pull of the Moon and the Sun are either working together or working against each other.
The moon causes tides. It also exerts enough force to change the movements of ice flowing in glaciers. So I would assume it affects the earth. This latest mega-earthquake occured during the full moon phase. The moon used to be closer to Earth long ago. Over the eons, it has moved away yet even though it is not that huge.
The Boxing Day event was on a winter solstice full moon. This event was right before Easter, the full moon of the Spring Equinox. Looking at the other planets, one can't help but notice they are not like our earth. We know that the tidal pull of the Jovian giants heat up their moons but perhaps because our moon is so big compared to our own size, it has caused our own planet to stay hot?
For Mars is a geologically dead planet with two very minor moons that can't do much. The earth's surface probably oozed and moved about so forcefully due to the pull of the moon as it caused the water on the planet's surface to shove the continents and cause cracks in the lithosphere that would allow the hot magma of the mantle to escape and pour forth.
Perhaps our fractured surface was caused by lunar tides? And everything is lopsided due to the fluidity of the oceans? This brings to mind a new thought: during the last 5 million years, during the increasing Ice Ages, were the Northern continents pinned down by the ice and did this slow them down while Australia and India were both free of ice and free of Antarctica, the landmass they calved off from---did they and Africa move freely while the rest of the planet slowed down?
Is this why they are still moving forcefully even as both crashed into or are skirting past, Asia? And Africa is moving into Eurasia so forcefully, it is splitting apart on the east coast, cut by the Arabian Penninsula like a cake being cut by a sharp knife?
Looking at this simplified gravity map I drew, it is interesting to see that the main 'hot spots' are where Australia is riding up over the Pacific Plate and has deformed the southern edge of the Asian Plate very badly, there is severe subduction zones along the entire front as the Australian Plate slides under Asia even as Australia slides OVER the Pacific Plate. The world's biggest earthquakes and some of the most active volcanoes are along this subduction zone. Yet Australia itself is serene with no volcanoes and no earthquakes.
Why is this? The gravity map also shows interesting things like the fact that the lithosphere on either side of the Himalayans has collapsed. Geologists last month suggested the lithosphere fell away entirely under the Tibetan Plateau. This looks like it should be a good analysis.
The other place where the crust is very thin is the Indian Ocean right below India. This weak spot is very noticable, it is part of the Australian plate and it is one of the biggest thin areas on earth. This seems odd to me since it is also being shoved relentlessly and rather swiftly, under Asia. One would imagine it would be bulking up due to hitting something hard.
Here is the gravity map of Australia. It is quite interesting that the western half is 'thin crust' with a hidden element: looks like the remains of a subduction zone in the southwest corner. According to some geologists, the western half of the continent was dry land while the eastern half was under water. Yet the eastern half, in these gravity data pictures, is the denser sector and the middle of the western half is thinner? A riddle indeed.
One wonders if the lithosphere fell there, causing the land to spring up over the Pacific Plate? What I mean is, the dense lithosphere on the half riding next to Southeast Asia has been very stressed by this and the lithosphere seperated and now the western half of Australia is riding up over the plates that are moving in the opposite direction? There are some older fault lines along the Southwestern Wales.
I also wonder if these gravity maps show past asteroid hits? From before there was life on earth, even.
The complex earth is very challengeing to understand and geologists have a really fun job, figuring out what is going on. The theories abound. This latest huge earthquake happened at that interesting depth of 10 km. The Boxing Day Tsunami occured on that depth, too. Many important quakes are at that depth.
So what is going on there between the crust and the lithosphere?
Steven E. Ingebritsen*, and Craig E. Manning
Nearly all of our data below about 10-km depth represent permeability during prograde (heating stage) metamorphism. This finding suggests that the deeper part of this k-z curve is most applicable to regions where the crust is being thickened and/or heatedthat is, to orogenic belts. There appears to be a causal link between fluid sourcing and permeability in tectonically active crust (9, 10); for example, metamorphic devolatilization reactions likely generate porosity waves that progagate upward through the crust from the zone of fluid liberation (13). In the absence of a fluid phase, permeability and porosity in the middle and lower crust may be exceedingly small. Thus we expect lower permeabilities during cooling and decompression, or in the deep crust in stable cratons, where there is no active metamorphism.
It has been proposed that there is a hydrologic seal or that permeability decreases markedly at the brittle-ductile transition (14-16), which occurs at 10- to 15-km depth in crustal rocks under geothermal gradients typical of regional metamorphism. Such behavior would retard or prevent transfer of fluids from the deep crust and mantle to the upper crust and hydrosphere. However, our data indicate a change in slope of the permeability-depth relation near the brittle-ductile transition, rather than an abrupt decrease in permeability. The log fit to the data (Fig. 1A) shows permeability decaying by about an order of magnitude below the brittle-ductile transition, but the data below about 12.5 km are actually fitted just as well by a constant permeability of 1018.3 m2 (Fig. 1B).
We know the moon has a lot of influence on the more fluid parts of our earth not to mention the bodies of all living things that have fluid which is why us females, for example, are in thrall to the moon and are aware of it's moods and quirks. So of course, the fluidity and temperature of the planet itself responds to the moon as well as the sun, of course, our ultimate ruling force.
The brittle–ductile transition has been suggested to provide a mechanical trap to deep crustal fluids. The mechanism was advanced as a way of reconciling the geophysical case for a wet lower crust, founded on the revelation of deep crustal electrical conductors and seismic reflectors, with the problem of maintaining interconnected, low-density fluids in stable crust for geologically significant timescales. Although some deep crustal conductors are now attributed to graphite, the hypothesis of fluid trapping at the brittle–ductile transition has been widely adopted in electromagnetic literature, with no regard to tectonic regime, and in association with standardized temperatures of 300–450°C. Meanwhile, petrologists continue to argue that the lower crust is dry.
This paper re-examines the arguments on which the hypothesis of fluid trapping at the brittle–ductile transition has been founded, and concludes that there is a geophysical case for a dry lower crust based on electromagnetic studies. The magnetotelluric (MT) technique yields electrical conductances (conductivity–thickness products) that are direction dependent (or anisotropic). The necessity of considering direction-dependent conductances, rather than a bulk conductance, is demonstrated using data from Saxothuringia, Germany. A quantitative model is developed to facilitate joint interpretation of the maximum conductance and the anisotropy of conductance (ratio of maximum to minimum conductance). The model yields quantitative arguments against fluids being the principal cause of deep crustal electrical conductivity, because unreasonably thick layers and unreasonably high porosities are required.
So the degree of vicosity and fluidity of this important level of the earth's crust is in full debate. I cannot judge which makes more sense and hope to see more data as researchers probe our own planet.
10 km seems to be a point where the fluidity of crustal rocks changes, it is where water and minerals can still vacillate between several states. Obviously, when earthquakes happen, there has to be some fluidity below or it woudn't happen.
I can't print up either of theses document above but they are interesting reading. I always wondered why most major quakes happen at that depth more often than any other. Thin crust or thick, it is the same.
Eric Debayle, Brian Kennett & Keith Priestley
Institut de Physique du Globe de Strasbourg, Ecole et Observatoire des Sciences de la Terre, Centre National de la Recherche Scientifique and Université Louis Pasteur, 61084 Strasbourg, Cedex, France
The depth configuration of azimuthal anisotropy beneath Australia in the depth range 150–300 km is similar to that beneath oceans in the depth range 50–200 km but shifted downward by 100 km. Except in the upper 100 km, Australia is completely different from other continents, which display a gentle decrease of anisotropy from 1.4% at 50 km to about 0.6% at 300 km depth.
Further, Australia is the only continental plate where azimuthal anisotropy correlates significantly with present-day plate motion. This peculiar behaviour of the Australian continent is highlighted in the global correlation (Fig. 3) between azimuthal anisotropy and the present-day absolute plate motion (APM). Fast anisotropy directions beneath Australia do not correlate with APM at depths shallower than 150 km, but show strong correlation from 150 km to 300 km depth with a maximum near 200 km. This agrees with previous regional surface wave tomography for the continent
None of the other continents show significant plate-scale correlation between anisotropic directions and APM. The anisotropic signature of the Australian plate is similar to that observed at shallower depths beneath oceans. In young oceanic regions where the lithosphere is expected to be thin, significant correlation between anisotropy and APM is observed at 50 km depth (Fig. 3) and extends over large regions around the mid-ocean ridges beneath the Pacific, Indian and Atlantic Oceans. At 100 and 150 km depth, the regions where anisotropy correlates with APM shift to the old oceanic basins. This shift suggests that the depth of plate-motion-induced deformation increases with the age of the sea floor and the thickness of the oceanic lithosphere.
Figure 2b shows the average correlation between APM and fast anisotropic directions calculated for Australia, other continents, and oceanic basins. The strong correlation between Australian anisotropy and APM is prominent between 150 and 300 km depth. The fast direction beneath the oceans displays, on average, a weaker correlation with APM between 100 and 250 km depth. This weaker correlation between oceanic anisotropy and APM can be related to the observation.
Our results therefore suggest that the Australian plate is the only continental plate whose motion is fast enough to produce large scale deformation at its base. The slower horizontal motion of other continental plates may produce smaller basal deformation, and thus a larger proportion of olivine crystals with a plunging axis of symmetry and a weaker azimuthal anisotropy. At depths greater than 220 km, enrichment in clinopyroxene may also contribute to the vanishing of anisotropy
I wonder if India was like Australia? It is from the same vector and moved at tremendous speed, much faster than anything else around it. Why would that happen? It nearly split in two before hitting Asia. The Deccan Traps are from a rift that opened, not from a collision but being yanked apart! This filled with lava and it killled of a tremendous number of life-forms across the planet.
Perhaps the base of Australia (and India) were detached from the lithosphere allowing them to flow with minimal friction? One can only guess. What we do know is, the leading edge of Australia is causing mountain building via volcanoes. But the buckling of the continent's leading edge is minor compared to the leading edge of North America that is violently buckling under the stress of trying to crash over the Pacific Plate, indeed, it is probably shoving that plate westards at a good clip, considering. Except this doesn't explain much of anything!
Why is the Pacific Plate moving so swiftly into Asia? It hits Asia and slides under with great violence. We know that Eurasia is moving towards the Pacific thanks to the Atlantic rifting. But why is it cartwheeling to this one point in the ocean that happens to be the same spot Australia is determined to head into? If I were looking at this as a dynamic system on a flat surface, I would suspect there is some magnetic force at work, if this were concave, I would suspec that is the lowest point.
But this is a globe and there is no singular reason for all the northern landmasses to move towards that spot. Heh. Maybe I should call it 'The Great Attractor' in honor of that mega-complex of galaxies that our own is heading towards at break neck speed!
It seems very reasonable to suppose that when sea levels rise or fall, they do so by the same amount everywhere - water after all finds its own level. Surprisingly, this is not the case in Australia. 120 million years ago, Eastern Australia was flooded with water creating a huge inland sea. Yet this flooding occured at a time when sea levels around the world were relatively low. To add to the confusion, Australia lost its inland seas about 70 million years ago when elsewhere around the world, sea levels were at their highest.
In 1998, Mike Gurnis from Caltech, Dietmar Müller from Sydney University, and I set out to solve the Australian flood conundrum using the modeling approach I have outlined. We took all the information which Dietmar Müller had compiled for the way the Australian plate had moved over the past 100 Million Years and combined this with a 3 dimensional model of the mantle which included cold slabs of lithosphere like the one shown in Figure 2.
We discovered that Australia passed over one of these slabs over one hundred million years ago as it was drifting Northward and Westward in response to far-reaching mantle flow patterns. 120 Million years ago, when Australia was considerably further South than it is today, and still attached to Antartica, the oceanic lithosphere to the East of Australia was sinking into the mantle and dragging down the Eastern half of Australia by up to three hundred metres - enough to cause widespread flooding despite globally low sea levels.
In Figure 3 the dark blue on the map of the Australian continent show our prediction of the flooded areas. Flooding persisted until about 60 million years ago. At this point, the sinking lithosphere was several hundred kilometers down in the mantle and its effect on the continent was beginning to weaken. At about this time Australia began to separate from Antarctica and move Northward. As it escaped from the influence of the sinking lithosphere, Eastern Australia popped back up again. Now, however, it was covered with a layer of sediments and stood higher than it had before the flooding occured. (Newly flooded land immediately starts to accumulate a layer of sediments from the erosion of nearby high-ground and from the action of the small creatures that live in the water).
This was enough to prevent the same areas from flooding again when global sea levels rose. What became of the sinking slab ? Most of it is now deep in the mantle where it is barely detectable by seismological probing. However, a small part of it was dragged near to the surface when Australia and Antarctica split apart. Today the ancient slab is located in between the two continents where it sucks the ocean floor down, causes very unusual patterns on the seafloor and an obvious change in the chemical makeup of the seafloor - a mysterious region known as the Australian-Antarctic discordance (or AAD for short). Our prediction of the location of this remnant of lithosphere is marked by the centre of the purple ellipse in the final frame of Figure 3; it is remarkably close to the true position of the AAD.
Yet another sinking lithosphere moment. I would suggest that far from uncommon, this is normal. Namely, our shattered lithoshpere, first banged up most terribly by some ancient collision, the one that created the moon, never go to form a solid like the ones on Mars and Venus not to mention the moon itself. All the planets and moons were hammered by space objects of various sorts to the point that the moon, for example, is wall to wall craters, but these didn't crack the lithospheres of the other planets and I would again, suggest the moon is responsible for keeping things cracked up here.
And every time a meteorite or asteroid or comet slams into the earth, the shaking this causes, especially when they hit the ocean or on a rift zone, can widen these cracks and activate them. The theories of these two geologists are intersting but don't refer to the gravity maps and this is the problem with theories: one has to include lots and lots of data and not leave out unhappy bits that don't fit.
And I think very few things explain Australia, why it is zooming northwards with such ferocity and why it is so 'quiet' geologically even as it is causing much of the earth to spasm with pain and annoyance. Why the earth is splitting along the Atlantic Central Ridge and between Antarctica and the India/Australian plates is a mystery still. Why are these areas so active? Why are they so powerful? What on earth is going on down there, the place earlier people called 'Hell'?
Who the hell knows.